The invention relates to an intervertebral implant having an upper and a lower supporting surface for abutment with adjacent vertebral bodies, having a concave dorsal longitudinal side, a ventral longitudinal side lying opposite the latter, having a rounded contour at the two end faces connecting the longitudinal sides and having at least one hole extending through the implant from the upper to the lower supporting surface.
Such an intervertebral implant is known, for example, from DE 297 20 022 U1. It is used, after removal of a disk, partially to fill the intervertebral space between two adjacent vertebral bodies and thereby support the adjacent vertebral bodies against one another. Besides the support function said implants are also intended to enable a bony fusion of adjacent vertebral bodies, which is why they only partially fill the intervertebral space; in the construction known from DE 297 20 022 U1 the implant is formed from relatively narrow side walls, which with their top and their bottom edge form only a small supporting surface for the adjacent vertebral bodies. When an intervertebral implant is used, which substantially takes the form of a solid body and only has holes for receiving the bone material, it is frequently difficult to introduce the bone material into said holes and into remaining free spaces of the intervertebral space.
The object of the invention is to design an intervertebral implant of the type described in such a way that even after insertion of the intervertebral implant into the intervertebral space it is still easily possible to introduce bone material into regions of the intervertebral space not occupied by the implant.
In an intervertebral implant of the type described initially, said object is achieved according to the invention in that in the region of the middle portion of the ventral longitudinal side at least one introduction channel for bone material, which extends through the implant, exits from the implant. The provision in the implant of such an introduction channel, which exits from the implant in the middle region of the ventral longitudinal side, makes it possible for bone material to be introduced through the inserted implant into the intervertebral space and disposed in the region of the intervertebral space ventrally adjoining the inserted implant, thereby ensuring that bony growth sets in immediately adjacent to the inserted implant and the implant is therefore fixed in its inserted position between the adjacent vertebral bodies.
It is advantageous if the introduction channel enters the implant in the part of an end face adjoining the dorsal longitudinal side. By said means bone material may be introduced dorsolaterally into the implant and may pass from the introduction side through the implant to the ventral side of the intervertebral space; in said manner access is therefore made considerably easier.
It is particularly advantageous if the introduction channel crosses a hole, which extends through the implant. Thus, the introduction channel may also be used to introduce bone material into the hole.
In a particularly preferred embodiment of the invention it is provided that the introduction channel at its ventral end has fastening elements for an instrument inserted into the introduction channel. The introduction channel therefore has a dual function, on the one hand it is namely used to fill the intervertebral space with bone material and on the other hand it may receive an instrument, which is used e.g. to manipulate the intervertebral implant and insert the latter into the intervertebral space. By means of the fastening elements the instrument may be firmly connected to the implant so that the surgeon may delicately guide the implant during insertion.
As a fastening element a bayonet catch, for example, might be used, it is particularly advantageous if the fastening element is formed by an internal thread.
The introduction channel preferably extends in a plane, which is disposed substantially parallel to the supporting surfaces.
In said case, the introduction channel may be inclined between 30xc2x0 and 80xc2x0 relative to a longitudinal axis of the implant in a plane extending substantially parallel to the supporting surfaces.
In a preferred embodiment, two introduction channels enter the implant from different end faces of the latter so that the introduction of bone material and/or the manipulation of the implant may be effected by inserting a manipulating instrument from the direction of both end faces.
It is particularly advantageous if the implant is constructed symmetrically relative to a centre plane perpendicular to the supporting surfaces and to the longitudinal sides, thereby allowing the implant to be inserted in two orientations.
In a preferred embodiment it is provided that two holes are disposed at the two ends of the implant adjacent to the end face of the latter.
In particular, the holes may have a circular cross section.
It is advantageous if the supporting surfaces are inclined, e.g. at an angle of between 0xc2x0 and 15xc2x0, relative to one another.
It may further be provided that the supporting surfaces carry projections, which assist the fixing to the adjacent vertebral bodies.
Said projections may be, for example, spike-shaped points or ribs.
It is particularly advantageous when the projections in the form of ribs extend along the edges of the holes. The holes are therefore surrounded by a rib-shaped collar, which may additionally comprise notches for improved connection to the adjacent vertebral bodies.
In another embodiment it is provided that the projections are microprojections, which are formed by a rough surface structure of the supporting surfaces. For said purpose, the supporting surfaces may be provided e.g. with a coating, which gives rise to a roughened surface structure comprising micropores.